Electric gauge



April 1941- c. M. HATHAWAY 2,240,184

ELECTRIC GAUGE Filed March 26, 1938 Inventor-z Claude Mfiathavyag,

f v v :3

b fib z V 9 His A ten-"neg.

Patented Apr. 29, 1941 moi-arc canes Claude M. Hathaway, Nlskayuna, N.Y., assignor to General Electric Company New York a corporation ofApplication March 26, 1938, Serial No. 198,837

8Claims.

My invention relates to electric gauges and concerns particularlyelectric gauges of the type in which the reluctance of the magneticcircuit is varied in response to variations in the quantity to begauged.

It is an object of my invention to provide improvements in apparatus andmeasurements for measuring various quantities, such as dimensions ofobjects, pressures, etc.

It is an object of my invention to provide electric gauging arrangementsof high sensitivity and low cost as well as to provide gauges which arehighly compact.

A further object of my invention is to provide convenience in operationand adjustment of electric gauging arrangements.

Still another object of my invention is to provide electric gaugingarrangements in which the operation is independent oi variations insupply voltage.

Another object of. my invention is to provide electric gauges havingsensitivity control and zero adjustment which are independent of eachother.

It is also an object of my invention to provide electric gauges in whichsensitivity-control is independent of both the supply voltage and thezero adjustment.

Other and further objects and advantages will become apparent as thedescription proceeds.

In carrying out 'my invention in its preferred form, I provide anelectric gauge head having a magnetic circuit including a pair ofelectromagnets with their magnetic flux paths in parallel and includingvariable air gaps. A movable armature is provided to form the edges ofthe air gaps so that movement of the armature produces oppositevariation in the lengths of the air gaps. The movable armature ismechanically connected to a spindle or member which moves in response tovariations of dimensions or other quantities being gauged. Theelectromagnets are connected in a circuit including a measuringinstrument urements of the quantity to be gauged.

The invention may be understood more readily from the following detaileddescription when considered in connection with the accompanying drawingand those features of the invention which are believed to be novel andpatentable will be pointed out in the claims appended hereto. In thedrawing, Fig. 1 -is an assembly view in elevation of one embodiment ofmy invention. Figure 2 is a side elevation of mechanism includ- 1.Figure 3 is a circuit diagram representing the electrical connections ofthe coils shown in Figure 2. Figure 4 is a modified circuit diagramsuitable for use with the apparatus of Figure 2,

and Figure 5 is another modified circuit diagram which may be used withthe apparatus 0! Figure 2. Like reference characters are utilizedthroughout the drawing to designate like parts.

Although my invention is not limited to apparatus for gauging dimensionsof mechanical pieces, such apparatus forms one oi its most valuableapplications, and in Figure 1 I have illustrated apparatus for measuringoutside dimensions of small parts such as blocks and rods. The apparatusof Figure 1 consists 0! a base ll carrying a removable platen l2 uponwhich a piece to be gauged may be placed. There is attached to the baseII a post I! carrying a gauge head it, with a movable spindle l4,adapted to come in contact with the upper surface of a piece restingupon the platen i2, so that the position of the spindle it within thegauge head l3, which is measured by the apparatus, depends upon thedimension of the piece being gauged. In order to adapt the gauge tomeasurement of pieces varying widely in dimensions, the gauge head l3may be adiustably secured to the post l2 by means of an adjustablesupport 15 arranged to slide vertically on the post l2 and including athreaded nut, not shown, adapted to cooperate with a screw l8 which maybe turned by hand with a crank H. For tightening the adjustable supportI! at any given position on the post l2, a clamping screw 18 may beprovided.

The gauge head I! as shown in Figure 1 is mounted in a casing with onlythe spindle I4 projecting. The apparatus within the casing which isshown in Figure 2 is carried by a non-magnetic base is which may beproduced by die-casting, and is secured in any suitable manner to theadjustable support I! of Figure 1. The spindle H which, in thearrangement illustrated is placed 'ver-tically, is carried by avertically movable carrier block 20 composed of magnetizable materialwhich is movably secured to the base I! by means of springs 2| composedof magnetizable material. In order to increase the stiiiness' oi thesprings 2| and in order to maintain the carrier block 20 insubstantially absolute rigidity with respect to'lateral motion eitherperpendicular or parallel to the base i9, reinforcing plates 22 areprovided which are secured to the springs 2| on either side thereof, andextend very nearly the distance between the points of attachment ed inthe gauge head of the apparatus of Figure of the springs 22 to thecarrier block 20 and 2 v the clamps 23 securing the springs 2i to thebase II.

The base II is formed with lugs 24, to which both the spring securingclamps 22 and horinontal brackets. 2! are secured. 'hvo double-coileleetromagnets 2i and 21 are secured to, and mounted between, thebrackets 2|, the electromagnet 20'be'ing suspended from the upperbracket 2| and the electromagnet 21 resting upon the lower bracket 2|.Brackets 2! as well as the clamps 22 are composedofmagnetizablematerial. The electromaanet 2' consists of two coils or windings 2| and20 wound around a core 30, and the electromagnet 21 consists of twocoils 8i and 22 wound around a core 20. The only portions 'of the cores2. and 22 which are visible are the pole tips which are spaced from eachother a sumcient amount to allow an armature I carried by the carrierblock 20 to be located therebetween and leave air gaps" and 26 on eitherside of the armature 34.

The electric gauge consists essentially of the gauge head havingelectromasnets 2i and 21 with the air gaps I! and "variable in responseto motion of the spindle I4 and means such as shown in Figure 3, 4 or 5for measuring the relative reluctances of the air gaps II and N.

The gauge head includes the base l9, carrier block 20 carrying thespindle II, a pair of electromagnets 2B and'2l and a movable armature 24carried by the block 20 in a position between electromagnets 2| and 21in order that movement of the spindle M will simultaneously decrease theair gap formed between the armature l4 and one electromagnet andincrease the air gap formed between the armature and the otherelectromagnet, so as to multiply or amplify the eiiect of spindlemovement on the electrical circuits of the apparatus.

In the arrangement represented by Figure 3, a source of regulatedvoltage is provided such as a voltage regulating transformer 31energized by a source of alternating current 28 and consistingessentially of a capacitor ll and a winding 40 in series. the winding llhaving a saturable core which is operated above the point of saturation.Thus if any variations in the voltage of the source ll take place,although the .current flowing through the winding II and the capacitor39 in series will vary, the flux in the core and the voltage induced inthe portion ll of the winding serving as the secondary will remainsubstantially constant. The regulated or substantially constant voltageprovided by the secondary winding I is connected to the coils 28, 29, 3|and 32 through a sensitivity-control rheostat 42. The coils 2B, 29, 3|and 32 are connected in series parallel to form a Wheatstone bridgecircuit. The diagonal arm of the Wheatstone bridge circuit is formed byan alternating current-responsive device such as a rectifier voltmeter43 consisting of a direct current-responsive instrument N and fourrectifiers such as copper oxide rectiflers l5, l8, 4! and 48, forexample, arranged in the wellknown full-wave rectifying connection. Thetwo coils of each electromagnet are so connected as to be diagonallyopposite arms of'the electrical bridge in order that variations in theair gaps will produce opposite variations in the reluctances of themagnetic circuits and of the reactances of adjacent coils in the bridgefor the purpose of magnifying the unbalance of the bridge produced bythe spindle H. Furthermore, the connections are preferably such thatvoltages of corresponding polarity are induced in all the coils in the-case, -the coils 2| and II bridge. The polarities at a given instantare represented by and signs in i ure 3- ItwillbeobservedthatinbothfiguresSandi the coils 2| and 20 of the magnet 2! arediagonally opposite arms of the bridge and the coils 2| and 82 of thismagnet 21 are opposite arms of the bridge. However, in one are lowerarms of-the bridge and in the other case they are the right hand arms ofthe bridge. I have found either arrangement of the coils in the bridgeto be satisfactory. The turns of the coils are wound in such a directionthat two flux paths are formed joining at jthe center of the block 2|and running parallel through the armature N. In order to facilitatesetting the instrument ll to zero ,when the spindle I4 is in a positioncorresponding to the standard dimension from which deviations are to bemeasured, the zero adjustment potentiometer 48 is provided in one arm ofthe bridge between the coils 2i and Ii. In the arrangement of Figure 3apotentiometer tap llslidable along the potentiometer Iii serves as oneof the connections to the current responsive unit 43.

Figure #3 illustrates the Wheatstone bridge formed by the electricalcircuits of the coils 28, 29, li and I2. The arrows in Figure 2represent the magnetic circuits of the coils 28, 2|, 2| and 32. One suchmagnetic circuit may be traced from the top surface of the armature 34through the coil 29, thence through the coil 22, the upper brackets 25and 23, the spring 2i. and the upper half of the carrier block 2. backthrough the armature H. The other magnetic circuit may be traced throughthe coils 2i and I2, the lower brackets 25 and 23, the lower spring II,the lower half of the .block 2|, back through the armature 34. It willbe observed that the magnetic circuit of the coil 20 consists of the airgap 35 and a portion of the core 2| surrounded by coil 2!, and that themagnetic circuit of the coil 3i consists of a portion of the core iswithin the coil II and the air gap 88. However, the greater portion ofthe reluctances is represented by the variable air gaps l5 and 38. Thus,when the spindle ii is in such a position that the air gaps [5 and IIare equal, substantially equal fluxes cross these air gaps since thecells 29 and II are arranged substantially symmetrical in the electricalcircuit, and normally carry like currents, but when the air gaps becomeunequal, the reluctances become unequal in an exaggerated degree due tothe fact that, in the firstplace, the reluctance of an air space isinversely proportional to its length and,

secondly, if the magnetic material is operated in the portion of themagnetization curve below the point of maximum permeability, with theunbalancing of the magnetic circuits when the fluxes become unbalanced,the permeabilities of the cores become unbalanced and thus furtherunbalance the reluctances. Inasmuch as the reactances of the coils areinversely proportional to their reluctances, movement of the spindle i4produces a greatly exaggerated unbalance oi the potential drops in theelectrical Wheatstone bridge circuit.

The instrument 44 may be calibrated in terms of the deviation of thespindle I 4 from its normal position, in other words, in terms of thedimen'sions of a block or other piece to be gauged and which is placedon the platen l2 under the spindle H. In the arrangement of Figure 3,the sensitivity of the apparatus may be adjusted by changing the settingof the rheostat 42 so that a also diagonallygiven deviation from anormal dimension produces a greater or less deflection of the instrument44 and of course, other deviations from standard produce in proportiongreater or less deflections. 'The zero adjustment is made by placing astandard piece on the platen under the spindle l4 and moving the tap Iin one direction or the other until the instrument 44 reads zero.

Rectifiers of the dry type operate more nearly perfectly as rectitlerswhen they are carrying a given amount of current, and a moresatisfactory scale distribution of the scale 44 may, therefore, beobtained by utilizing a suppressed zero instrument, as the instrument44, that is, an instrument which reads zero when it is actually carryinga current. If such a suppressed zero instrument is utilized it will beunderstood, of course,

that the zero adjustment potentiometer 49 a so set that the Wheatstonbridge is actually slightly unbalanced when the instrument 44 reads zeroor a standard dimension, if it is calibrated in terms of dimensions. Itthe instrument 44 is carrying current when it reads zero, it will beapparent that changing the'setting of the sensitivity-control rheostat42 will vary the current carried, and therefore, upset the zeroadjustment. Accordingly, zero adjustment should be made after thesensitivity-control adjustment has been made.

In order to make the sensitivity-control and the zero adjustmentindependent of each other, the circuit of Figure 4 may be employed inwhich no voltage regulator or constant output voltage transformer isnecessary to maintain constancy of the zero setting during operation. Inthis case, an ordinary transformer Si is employed having two secondarywindings 52 and 53. The coils 28, 29, 3| and 32 in the gauge head arearranged in the manner of a Wheatstone bridge as before, and connectedto the secondary winding 52. The cross arm of the Wheatstone bridge alsoconsists of a full-wave rectifier 43 as before; the ouput side of therectifier 43 feeds into the measuring instrument; However, the circuitof Figure 4 differs from that of Figure 3 in that a measuring instrument54 of the zero center type is employed, and the instrument 54 receivescurrent not only from the rectifier 43, but also from a second rectifier55 energized by the other secondary winding 53 of the transformer 5|.The rectifier 55 is similar in type to the rectifier 43, consisting offour copper oxide rectiflers '56, 51, 58 and 59. The rectifiers 43 and55, however, are connected so as to have opposite polarities withrespect to the instrument 54 and, consequently, no current flows ininstrument 54 and it stands at zerowhen the outputs of the rectiflers 43and 55 are equal.

For control of sensitivity, a sensitivity-control rheostat 60 isprovided which is connected in the primary side of the transformer 5|instead of in the secondary side. For setting the instrument 54 at zero,a zero adjustment rheostat 5| is provided which is connected in serieswith the secondary winding 53- of the transformer 5| In case thecurrent-resistance characteristics of the rectiflers 43 and 55 shouldnot be equal, the rectifier balancing potentiometer 62 is providedhaving a movable tap 53, to which one connection of the instrument 54 ismade.

Since the rectifiers 43 and 55 are balanced against each other, and theinstrument 54 normally carries a zero current for its zero setting, itwill be evident that voltage variations of the source 33 will not afiectthe zero setting because, regardless oi. primary voltage of thetransformer II, the outputs of the rectiflers 43 and will tend to flowwith equal strengths in opposite directions in the instrument 54. Inmaking initial adjustment of the apparatus, the zero adjustment rheostatBI is adjusted until the instrument 54 reads zero, whereupon the outputvoltage of the primary side of the transformer 5| is varied by varyingthe'adjustment of the sensitivity-control rheostat II to make sure thatthe instrument 54 remains at zero. If the instrument 54 should deflectfrom its zero setting it would be an indication that thecurrent-resistance characteristics of the rectiflers 43 and 55 didnot-quite balance, in which case, the tap 83 of the rectifier balancingpotentiometer 62 would be moved one way or the other until theinstrument 54 retained its zero setting regardless of ,the voltageapplied to the primary side of the transformer 5|. Having adjusted thepotentiometer 32 and the zero adjustment rheostat 5|,

the sensitivity adjustment is made by placing an object of knowndeviation from standard dimensions between the platen |2 and the spindlel4 and adjusting the rheostat 6|! to give the desired reading of theinstrument 54. Maximum sensitivity will obviously be obtained with aminimum amount of resistanc in series with the current source 33.

From the foregoing explanation of the operation of Figure 4, it hasbecome apparent that fluctuations in the voltage of the source 38 wouldcause the sensitivity of the measurement to fluctuate likewise. I! it isdesired to make sensitivity independent of voltage fluctuations acircult such as that of Figure 5 may be utilized in which thesensitivity is likewise independent of the zero adjustment. In thearrangement of Figure 5, varying the sensitivity tends to affect thezero setting. However, this is a matter of minor consequence since, thezero setting may readily be adjusted after each change in the desiredsensitivity, and it isoi. most importance that the sensitivity should beindependent of the zero adjustment. In the arrangement represented byFigure 5, a voltage regulating transformer 31 is employed again.However, in this case the transformer 31 is provided with two secondarywindlugs 52 and 53, analogous to the arrangement of Figure 4. Thesensitivity-control rheostat 42 of Figure 3 is employed, which isconnected in series with the input to the Wheatstone bridge formed bythe coils 28, 23, 3| and 32, and the zero adjustment rheostat 5| ofFigure 4 is employed as well as the feature described in connection withFigure 4 of employing a zero center instrument 54 fed by two oppositelyconnected fullwave rectifier-s 43 and 55, the output sides of which areconnected respectively to the Wheatstone bridge formed by the coils 28,29, 3| and 32, and the secondary winding 53 of the transformer 31. Apotentiometer for balancing rectifier characteristics such as that shownat 62 in Figure 4 may also be used in Figure 5 if desired.

In the arrangement of Figure 5, since a voltage regulating transformeris employed, the output voltages of the secondary windings 52 and 53remain constant regardless of variation of the voltage of the source 38,and therefore, neither the sensitivity nor the zero setting of theapparatus is affected by fluctuations in supply voltage. In adjustingthe apparatus, the approximate zero setting is obtained by means of therheostat 6|, by placing 'an object of standard dimension in the gauge.Sensitivity adjustment is made by placing an object of known deviationfrom the standard dimension in the gauge, and adjusting the rheostat Ito give the desired reading of the instrument ll, whereupon the standardobject is replaced in the gauge and the final zero adjustment is made bymeans or the rheostat Ii. Since the sensitivity of the apparatus isindependent of the zero adjustment, it will be unnecemary to reldjustthe rheostat 42.

I have herein shown and particularly described certain embodiments of myinvention and certain methods oioperation embraced therein for thepurpose of explaining its principle and showing its application but itwill be obvious to those skilled in the art that many modifications andvariations are possible and I aim, therefore, to cover all suchmodifications and variations as fall within the scope of my inventionwhich is defined in the appended claims.

What I claim as new and desire to secure by Letters Patent the UnitedStates is:

l. A gauge comprising a movable member, a pair or double-coilelectromagnets placed substantially end to end with pole tips spacedapart, an armature movably mounted between said pole pieces and of suchdimensions as to leave variable air gaps between said pole tips and saidarmature, a mechanical connection between said armature and said movablemember, and means responsive to relative magnitudes of the reluctancesof said electrom-agnets.

2. An electric gauge comprising a pair or double coil electromagnetseach having a core composed of magnetizable material with pole portions,an armature movable in response to variations in magnitude of a quantityto be measured and having a portion in proximity to the pole portion ofone of said electromagnets and another portion in proximity to the poleportion of the other of said electromagnets and spaced from said poleportions whereby air gaps are formed between said pole portions and saidarmature varying oppositely in response to movement of said armature, asource of current and a currentresponsive device, the coils of saidelectromagnets being connected in series parallel to said source 01'current, and said current-responsive device being connected :between thecommon points of the series pairs to form a diagonal arm of theWheatstone bridge.

3. In an electric gauge having four coils so arranged that the relativereluctances of two of the coils vary in response to variations in aquantity to be measured, the combination of a voltage regulatingtransformer having an input side adapted to be connected to a source ofalternating current, and an output side to which said coils areconnected in series parallel, a currentresponsive unit connected to thecommon terminals of the series pairs of said coils to form a diagonalarm of a Wheatstone bridge circuit, a sensitivity-control rheostatconnected in series with the outputside of said transformer and saidseries parallel coils, and a zero adjustment potentiometer consisting ofa resistor having a movable tap, said resistor being connected in seriesbetween the coils of one of said pair of series coils, and said tapforming a connection at one end of said bridge cross arm.

4. In combination four coils of an electric gauge so arranged that therelative reluctances of two of the coils vary in response to variationsin magnitude of a quantity to be measured, means for supplyingalternating current at substantially constant voltage, an alternatingcurrent-responsive unit and a zero adjustment potentiometer,

- two of said coils being connected in series, laid zero adjustmentpotentiometer being connected between the remaining two coils in seriestherewith, said series units being connected in multiple to said currentsupply source, and said currentresponsive unit being connected to thecommon terminaloisaidfirstpairoicoilsandtheadjush able tsp of saidpotentiometer to form the diagonal arm of a Wheatstone bridge circuit.

5. An electric gauge comprising i'our coils, means for causing therelative reluctances of a pair-oisaid coilstovaryinresponsetovariationsin a quantity to be measured, a transformer having a primary winding anda pair oi! secondary windings, a sensitivity-control rheostat, a zeroadjustment rheostat, a rectifying device having input and outputterminals, a second rectifying device having input and output terminals,a zero center current-responsive instrument, and arectying-characteristic balancing potentiometer including a resistor andan adjustable tap, the primary winding 01' said transformer beingadapted to be connected in series with the sensitivity-control rheostat,said gauge coils being connected in series parallel to one of thesecondary windings of said transformer, the input terminals of the firstof said rectifying devices be ing connected to the common terminals ofthe series pairs of said coils, whereby the first of said rectifierunits forms the cross arm oi. said Wheatstone bridge circuit, the sidearms or which are formed by said coils, the input terminals of thesecond or said rectifying devices being connected to the second of thesecondary windings of said transformer in series with said zero ad-Justment rheostat, one of the output terminals of one of said rectifyingdevices being connected to one 01' the output terminals or the otherrectifying devices and the resistor of said potentiometer beingconnected between the remaining output terminals, the connections beingsuch that terminals oi. opposite polarity are connected together, saidinstrument being connected between the first mentioned connected outputterminals 01' said rectifiers and the adjustable tap or saidpotentiometer.

6. A gauge comprising a pair of current conducting elements havingimpedances, the relationships of which are adapted to vary in responseto variations in a quantity to be measured, a second pair of impedances,said pairs of impedances being connected in series parallel with theinput terminals at either end of the series pairs, and output terminalsin the middle of the series pairs, a current-responsive device connectedto said output terminals, means for supplying voltage to the inputterminals of said parallel impedances, means for supplying voltage tosaid current-responsive instrument of opposite polarity to that suppliedby the output terminals 01 said series parallel circuit, and means formaintaining said latter applied voltage proportional to the voltageapplied to the input terminals of said series parallel circuit.

7. An electric gauge comprising a pair of coils connected in seriesadapted to have their relative impedances vary in response to variationsin a quantity to be measured, a pair of current carrying elementsconnected in series, a voltage regulating transformer having secondarywindings. a sensitivity-control rheostat, a pair of rectifiers eachhaving input and output terminals, a zero adjustment rheostat and acurrent-responsive unit, said coils and current carrying elements beingconnected in series parallel to one oi said secondary windings in serieswith said sensitivitycontrol-rheostat, the input terminals of one ofsaid rectifiers being connected between the common terminal of the saidcoils, and the common terminal of said current-carrying elements,whereby the rectifier forms andiagonal arm of a Wheatstone bridgecircuit, the input terminals of the second rectifier being connected tothe sec- 0nd of said secondary windings in series with said zeroadjustment rheostat, the output terminals of said rectifiers beingconnected together with the polarities in opposition and said currentresponsive'instru'ment being connected between the output terminals ofsaid rectifiers. v

8. A gauge comprising a pair of current carrying elements connected inseries, a second pair of current carrying elements also connectedinseries,'two of said current carrying elements being adapted to havetheir relative impedances vary in response to variations in a quantityto be measured, a pair of current supply means with a fixed relationshipbetween their voltages, said current carrying elements being connectedin series parallel to one of said current sources, a currentresponsiveunit in operative connection to the common point of one of said seriespair of current carrying elementsand to the common point 01 the other ofsaid pair of current-carrying elements, said current-responsive unitalso being in operative connection to the second of said current supplysources, the polarities of the voltages applied to said currentresponsive unit being

